Multi-media networks will require that a data flow be given certain QOS for a network connection. The recently proposed resource reservation protocol (RSVP) for IP (and signalling in ATM networks) is a way of requesting a particular QOS but pre-negotiation of this sort is foreign to the current data networking model and would require changes at the application level.
The major driving force behind the requirement for different QOSs in the data network is the need to introduce real time flows which have distinct limits in the tolerance to delay, and the variations in that delay. Interactive voice and video demand that the total delay does not exceed the threshold beyond which the human interaction is unacceptably impaired. Non-interactive voice and video streams which are being transferred in real time require that the maximum delay variation is bounded so that buffers can be kept to a reasonable size and guaranteed not to underflow. Meeting the delay requirements for real time flows usually means that these flows must be given priority over other traffic. This in turn brings in a requirement to limit the amount of such high priority traffic by some admission control policy to ensure that other classes of traffic do get some of the available bandwidth.
There are applications other than voice and video that can benefit from controlled latency. Network control traffic such as DNS transactions represent a small fraction of the total but will provide a much improved performance if treated with priority.
There is another class of traffic which does not have the tight requirements of voice or video but does involve human interaction with computers and can lead to noticeable decreases in productivity (or increases in frustration) if subjected to long delays. This traffic type is generated by applications such as X-Windows, Telnet and, more often now, world wide web browsing. This traffic can be protected from long queuing delays caused by bulk transfers such as FTP or NFS by allocating to it some guaranteed portion of the bandwidth as part of an output scheduling policy.
Even the bulk traffic can suffer from too much competition. Often a file transfer will be aborted after using much network resource because the overall time has exceeded the delay tolerance of the application or the user or management policies in intermediate servers. Also, when congestion causes packets to be dropped, it can easily impact many flows, and cause many resends. By guaranteeing a certain number of flows a minimum bandwidth and treating the remainder as best effort, it is possible to avoid spreading packet loss over so many flows and to reduce the number of aborted flows.
It would be much more acceptable if the QOS requirements were met by the network automatically and dynamically without the need for signalling. This would fit more naturally with the current IP networking paradigm.
Traditionally, Internet services (such as FTP, Telnet, NFS) are known only to the end systems and not to the network itself. The present invention allows the network to discover the nature of the service for each traffic flow, classify it dynamically and exercise traffic conditioning by means of such techniques as admission control and scheduling when delivering the traffic downstream to support the service appropriately. The scheduling separates real time traffic from other traffic by priority and allocates bandwidth between various classes of traffic. In conjunction with scheduling, the admission control guarantees performance. The scheduling also allows implementation of overlay administrative policies to give, for instance, certain groups different treatment than other groups. The classification need not emulate precisely the effect of pre-negotiated network connections but should provide similar improvements in service quality as seen by the users and the network.
It should of course be noted that in this specification the data network can also include any packet-based or cell-based networks, including ATM networks.